Abstract

The Yellow-breasted Chat, Icteria virens, is a member of the wood-warbler family, Parulidae, and exists as eastern I. v. virens and western I. v. auricollis subspecies. It is the only wood-warbler known to sing diurnally and nocturnally.

One objective was to determine whether the eastern and western subspecies produce songs that differ acoustically; another was to determine whether a western population of Chats in Nebraska produces songs that differ acoustically at dawn and at night. Properties measured were maximum frequency, maximum power, notes/second, singing rate, and % time singing. In addition, the inter-song interval and % whistle notes were measured in dawn/night song.

Recordings were obtained from Borror and Cornell Laboratories; 2,429 western and 2,434 eastern songs were analyzed. Two-way ANOVA revealed that the larger western subspecies, in more open habitats, had higher maximum frequency at dawn and day (P<0.05); maximum power was 25x greater in western song at day vs. dawn (P<0.0001); for dawn song, eastern maximum power was greater than western (P<0.0001). No differences were found in notes/second, singing rate, % time spent singing (P>0.05). The relationship between body size and song frequency was unexpectedly inversely related, indicating that the denser eastern habitat was more influential on song than size.

Recordings of 3,469 dawn and night songs from five male western Chat subspecies were analyzed. ANOVA revealed that Chats used significantly lower mean song frequencies and longer inter-song intervals at night (P<0.05). The lower frequencies are believed to be ecologically functional for long distance communication in attracting night-migrating females. Whistle notes occurred at night (15% per male), but were not recorded from any male in dawn song; whistles degrade less with distance and may be important in mate attraction. Inter-song intervals were longer at night (P<0.05), possibly allowing males to listen for female responses.

Overall, the results indicate that Chats vary certain components of their song depending on geographic location and time of day.